1. Field of the Invention
The present invention relates to thin-film magnetic heads provided with a coil layer formed between core layers. In particular, the present invention relates to a thin-film magnetic head which has an upper core layer having an improved shape and can meet trends towards narrow tracks, and relates to a method for making the same.
Also, the present invention relates to a thin-film magnetic head which is provided with a coil layer formed between core layers and has satisfactory NLTS (nonlinear transition shift) characteristics and OW (overwrite) characteristics.
2. Description of the Related Art
FIG. 10 is a longitudinal cross-sectional view of a conventional thin-film magnetic head. The left end of the thin-film magnetic head in the drawing faces recording media. This thin-film magnetic head is a so-called xe2x80x9ccomposite thin-film magnetic headxe2x80x9d having a reading head hi using a magnetoresistive effect and an inductive head h2 for writing signals onto recording media, such as a hard disk. The inductive head h2 is deposited on the reading head h1. This thin-film magnetic head is provided at the end of the trailing side of a slider of a floating-type magnetic head.
The reading head hi h as a lower core layer 1 composed of a magnetic material having high permeability, for example, a Fexe2x80x94Ni alloy (permalloy). The lower core layer 1 also functions as an upper shielding layer of the reading head h1 by means of the magnetoresistive effect.
A gap layer 2 composed of a nonmagnetic material, such as alumina (Al2O3), is provided on the lower core layer 1. As shown in FIG. 10, an insulating layer 3 composed of a resist or an organic resin is formed on the gap layer 2. Furthermore, a spiral coil layer 4 composed of a highly conductive material such as copper is formed on the insulating layer 3 so as to surround a base section 6b of an upper core layer 6. In FIG. 10, the coil layer 4 can be partially seen.
An insulating layer 5 composed of a resist or an organic resin is formed on the coil layer 4. The upper core layer 6 is formed by plating a magnetic material such as permalloy on the insulating layer 5. A front end section 6a of the upper core layer 6 is bonded to the lower core layer with the gap layer 2 provided therebetween to form a magnetic gap having a gap length Gl1. The base section 6b of the upper core layer 6 is magnetically coupled with the lower core layer 1 through cavities formed in the gap layer 2 and the insulating layer 3.
FIG. 11 is a plan view of the thin-film magnetic head shown in FIG. 10. The upper core layer 6 consists of a leading region A having a constant width and a trailing region B gradually spreading from the leading end region. The leading region A of the upper core layer 6 is slender and has a width which is equal to the track width TW.
In the inductive head h2 for writing, recording currents flowing in the coil layer 4 induce recording magnetic fields in the lower core layer 1 and the upper core layer 6. Leakage magnetic fields from the magnetic gap section between the lower core layer 1 and the front end section 6a of the upper core layer 6 record magnetic signals on recording media, such as a hard disk.
As shown in FIG. 10, the reading head h1 includes a lower shielding layer 7 composed of a magnetic material, a magnetoresistive element layer 9 formed on the lower shielding layer 7 with a lower gap layer 8 provided therebetween 8, and an upper shielding layer or lower core layer 1 formed on the magnetoresistive element layer 9 with an upper gap layer 10 provided therebetween.
NLTS characteristics and OW characteristics, as important recording characteristics, greatly depend on the shape of the leading region A of the upper core layer 6. Herein, the NLTS (nonlinear transition shift) characteristics mean the phase lead caused by non-linear distortion of the leakage magnetic field, generated in the magnetic gap between the upper core layers 1 and the lower core layer 6 of the inductive head h2 in FIG. 10 by the leakage magnetic field from the magnetic recording signals which are just recorded on a recording medium towards the head.
The OW (overwrite) characteristics mean a difference in output of recorded signals at a low frequency between the initial output before overwriting at a high frequency and the decreased output after the overwriting.
When the leading region A of the upper core layer 6 is slender, as shown in FIG. 11, the length L1 of the leading region A is considered to be preferably in a range of approximately 4 xcexcm to 10 xcexcm. Such a length L1, however, causes deterioration of OW characteristics although it contributes to improvement in NLTS characteristics.
The upper core layer 6 of the thin-film magnetic head is formed by a frame plating process, as shown in FIG. 12. In this-process, the coil layer 4 is formed and is covered with the insulating layer 5. An underlying layer 7 composed of a magnetic material such as a NiFe alloy is formed over the gap layer 2, exposed in the vicinity of the end, and the insulating layer 5. After a resist layer 8 is formed on the underlying layer 7, the resist layer 8 is exposed and developed to form a pattern of the shape of the upper core layer 6. A magnetic layer (upper core layer 6) is plated on the exposed underlying layer 7. The residual resist layer 8 is removed to form the upper core layer 6. The thin-film composite is cut along line Zxe2x80x94Z in FIG. 12 to form the thin-film magnetic head shown in FIG. 10, wherein the cut surface along line Zxe2x80x94Z faces the recording media.
Production of the upper core layer 6 of a conventional thin-film magnetic head has the following problems. FIG. 13 is a plan view when a resist layer 38 is formed on the underlying layer 7 and a pattern 39 of the upper core layer 6 is formed on the resist layer 38. As shown in FIG. 13, the pattern 39 of the upper core layer 6 consists of the leading region A having a track width TW at the left side in the drawing and the trailing region B spreading towards the right side. The current track width TW, approximately 2 to 3 xcexcm, of the leading region A must be decreased to 1 xcexcm or less in order to meet current high-density recording trends.
The pattern 39 is formed by exposing and developing the resist layer 38. In conventional processes, the slender leading region A and the spreading trailing region B are simultaneously exposed using short-wavelength light (g-line to i-line) at a low NA (numerical aperture) of 0.2 to 0.3 for achieving a large depth of focus. For example, the upper limit of the resolution is 1.0 xcexcm for a combination of the i-line and a numerical aperture NA of 0.2 to 0.3. Thus, a track width TW of less than 1.0 xcexcm is not achieved in conventional processes.
When the resist layer 38 on the leading region A is removed in the development step after the formation of the pattern 39 for the upper core layer 6, a developing solution barely penetrates into the resist layer 38 in the pattern 39 for the slender leading region A having a small width (track width TW). Thus, the resist layer 38 in the leading region A may be not completely removed. Accordingly, this process is not applicable to an upper core layer having a smaller track width TW.
In addition, the leading region A of the resulting thin-film magnetic head has a small track width TW and a large length L1. Thus, OW characteristics are decreased by damping of the magnetic flux density in the leading region A. It is known that the OW characteristics of the upper core layer 6 having the leading region A with the track width TW decrease as the length L1 of the leading region A increases.
It is an object of the present invention to provide a thin-film magnetic head having an improved leading edge of an upper core layer to meet narrow track width requirement without deterioration of OW characteristics and to provide a method for making the thin-film magnetic head.
It is another object of the present invention to provide a thin-film magnetic head having an improved leading edge of an upper core layer to improve OW characteristics while maintaining satisfactory NLTS characteristics.
In accordance with a first aspect of the present invention, a thin-film magnetic head includes a lower core layer composed of a magnetic material and an upper core layer composed of a magnetic material formed on the lower core layer with a nonmagnetic gap layer formed therebetween, wherein the lower core layer and the upper core layer are opposed on an opposing surface facing a recording medium. The upper core layer consists of a leading region extending from the opposing surface towards the rear portion away from the recording medium and having a track width TW, a middle region extending from the leading region towards the rear portion and having a width larger than the track width TW, and a trailing region extending from the middle region towards the rear portion and having an increasing width. Furthermore the edges at the boundary between the leading region and the middle region are rounded.
In accordance with a second aspect of the present invention, a thin-film magnetic head includes a lower core layer and an upper core layer composed of a magnetic material, and a coil layer provided between the lower core layer and the upper core layer for inducing a recording magnetic field to the lower core layer and the upper core layer. The upper core layer consists of a leading region extending from an opposing surface facing a recording medium towards the rear portion away from the recording medium and having a constant track width, a middle region extending from the leading region to the rear portion and having an increasing width, the edges of the middle region having an angle of xcex81 with respect to the edges of the leading region, and a trailing region extending from the middle region towards the rear portion and having an increasing width, the edges of the trailing region having an angle of xcex82 with respect to the edges of the leading region.
Preferably, the angle xcex82 of the edges of the trailing region is larger than the angle xcex81 of the edges of the middle region.
Preferably, the angle xcex81 of the edges of the middle region is in a range of 5xc2x0 to 30xc2x0.
In accordance with a third aspect of the present invention, in a method for making a thin-film magnetic head including a magnetic lower core layer, a nonmagnetic gap layer formed on the lower core layer, and a magnetic upper core layer formed on the gap layer, the method includes the steps of forming the gap layer on the lower core layer, forming a coil layer on the gap layer at a position behind an opposing surface facing a recording medium, and then forming an insulating layer on the coil layer; forming a magnetic underlying layer over the gap layer exposed in the vicinity of the opposing surface to the insulating layer at the rear portion, and then forming a resist layer on the underlying layer; forming, by an exposing and developing process, a pattern for a middle region of the upper core layer in the resist layer lying at a region towards the rear portion with a given distance from the opposing surface, the middle region having a constant width larger than the track width, and a pattern for a trailing region lying towards the rear portion, the trailing region having an increasing width towards the rear portion, and simultaneously forming a pattern for a dummy region in the resist layer lying at a region towards the front section with a given distance from the opposing surface, the dummy region having a width larger than the track width; forming, by an exposing and developing process, a pattern for a leading region of the upper core layer in the resist layer between the pattern for the middle region and the pattern for the dummy region, the leading region having a constant width smaller than the width of the dummy region so that the pattern for the leading region connects the pattern for the middle region and the pattern for the dummy region; forming a magnetic layer in the patterns for the leading region, the middle region, the trailing region and the dummy region by a plating process, and then removing the residual resist layer; and removing the magnetic layer formed in the pattern for the dummy region and the magnetic layer formed in the pattern for the leading region lying in front of the opposing surface to expose the leading region, having the track width TW, of the upper core layer.
Preferably, the numerical aperture NA when the pattern for the leading region of the upper core layer is exposed is higher than the numerical aperture NA when the patterns for the middle region and the trailing region of the upper core layer and the pattern for the dummy region are exposed.